- Slides: 33
The Theory of Evolution …Evolutionary theory is a unifying principle in Biology. …Evolution, originally defined as descent with modification, or change in the characteristics of populations over time, currently defined as changes in allele frequencies over time.
The Theory of Evolution DARWIN PROPOSED A MECHANISM FOR EVOLUTION n The idea that life has evolved over time was not first conceived by Charles Darwin. n What was not known at Darwin’s time was how species evolve. n Charles Darwin came up with the mechanism or an explanation of how evolution occurred. - This mechanism was NATURAL SELECTION. n Darwin was the son of a doctor was born into a privileged family. n He went to Cambridge, got a degree in theology, but was more interested in the natural sciences.
How is Evolution different from Natural Selection? n Natural selection is a means of evolution
A little History n Many Theories for how the organisms and the world we know came to be. n Evolution was postulated by Buffon (all living things change over time), Erasmus Darwin and Lamarck before Charles Darwin was even born.
Charles Darwin’s Influences: n Charles Lyell – suggested earth was much older than previously thought n Thomas Malthus – suggested that human populations will grow beyond the space and food needed to sustain it. n Lamarck– proposed a mechanism that explained how organism change over time.
The Theory of Evolution DARWIN PROPOSED A MECHANISM FOR EVOLUTION n At the young age of 22 he was recommended to serve as a naturalist aboard the HMS Beagle. The experiences and observations he made on this voyage had a great impact on Darwin, especially a stop at the Galapagos Islands.
The Theory of Evolution DARWIN PROPOSED A MECHANISM FOR EVOLUTION n Much of his theory were derived from his observations in the variation amongst species of finches.
The Theory of Evolution DARWIN PROPOSED A MECHANISM FOR EVOLUTION Charles Darwin proposed that evolution occurred as the result of natural selection, a process resembling the artificial selection practiced by breeders of plants and animals. The ideas of Darwin's theory: 1. Variation exists within (the genes of) every population or species (the result of random mutation). 2. In particular environments, some individuals of a population or species are better suited to survive (as a result of variation) and have more offspring (natural selection). 3. Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population. 4. There is clear proof from the fossils and many other sources that living species evolved from organisms that are extinct.
The Theory of Evolution DARWIN SOUGHT A REASONABLE EXPLANTATION FOR EVOLUTION n Population – group of individuals that belong to the same species, live in the same area, and breed with others in the group. n Natural Selection – process by which populations change in response to their environment as individuals better adapted to the environment leave more offspring than those individuals not suited to the environment. Natural Selection at Work
B) Adaptations – process of inheriting traits that improves the chance of survival and reproduction of an organism 1) kinds of adaptations: camouflage and mimicry
The Theory of Evolution DARWIN SOUGHT A REASONABLE EXPLANTATION FOR EVOLUTION
The Theory of Evolution DARWIN SOUGHT A REASONABLE EXPLANTATION FOR EVOLUTION n With each generation, some individuals are better fitted to survive than others because of variation in characteristics. n Those individuals better fitted to survive in their environment are more likely to live long enough to reproduce. “Survival of the fittest. ” n Reproduction and transmission of the favorable variations that enabled their parents to survive and reproduce and to continue. n These favorable variations are called adaptations.
The Theory of Evolution DARWIN’S IDEAS HAVE BEEN UPDATED n Isolation – condition in which two populations of a species are separated so that they cannot interbreed.
The Theory of Evolution DARWIN’S IDEAS HAVE BEEN UPDATED Isolation n A geographical barrier, such as a body of water or a mountain range, may separate two populations of the same species. n The two populations do not interbreed because of their isolation from each other. n Different environments cause certain genes to be selected. n Overtime, the isolated populations may diverge so much that they lose their ability to interbreed successfully, even if brought together.
The Theory of Evolution DARWIN’S IDEAS HAVE BEEN UPDATED n Extinct – term used to indicate species that have disappeared permanently.
The Theory of Evolution FOSSILS PROVIDE OBJECTIVE RECORD OF EVOLUTION n Paleontologists – scientist who studies fossils. n Fossil Records: A Fossil is any remains or trace of a once-living organism. Types of Fossil formation are: – Preservation of whole organisms – Preservation of hard parts such as shells and bones – Petrifaction – Sedimentation
The Theory of Evolution BIOLOGICAL MOLECULES CONTAIN A RECORD OF EVOLUTION Comparative Biochemistry. n The composition and structure of a biochemical compounds in different species that can be compared. n It is found that in species that seem to be closely related by other evidence, that these compounds are also very similar in detail. – Examples: genes sequence, amino acid sequence of certain proteins like hemoglobin or chlorophyll in plants.
The Theory of Evolution BIOLOGICAL MOLECULES CONTAIN A RECORD OF EVOLUTION
The Theory of Evolution ANATOMY AND DEVELOPMENT SUGGEST COMMON ANCESTRY n Vestigial Structures – structure reduced in size and function; considered to be evidence of an organism’s evolutionary past. Ex-appendix,
The Theory of Evolution ANATOMY AND DEVELOPMENT SUGGEST COMMON ANCESTRY n Homologous Structures – structures that show common ancestry.
The Theory of Evolution n Gradualism – model in evolution in which gradual change over a long period of time leads to species formation. n Punctuated Equilibrium – model of evolution in which short periods of rapid change in species separated by long periods of little or no change. – In actuality Evolution is probably a result of both Gradualism and Punctuated Equilibrium or combination of each.
The Theory of Evolution The Case of Industrial Melanism – English Peppered Moth During the period when the number of coal-burning factories in England was increasing (during the socalled Industrial Revolution) it was noticed that the number of melanic (black) individuals of the species of Peppered Moth (Biston betularia) was becoming more common. Originally rare in the population of normally light-colored moths, the frequency of the melanic form increased in polluted areas until it was over 90%. This change in color has come to be known as "industrial melanism. " The change was presumed to be a result of natural selection since the melanic moths in polluted areas better matched the blackened tree trunks where they rested during the day. In unpolluted forests distant from industrial centers the tree trunks were not blackened and the lighter colored moths were present in higher frequencies. We know that the difference between the two forms of moth is controlled by a pair of alleles at a single chromosome locus.
Studies of Natural Selection 1) Industrial melanism in peppered moths
2) Insects developed a gene for resistance to DDT (pesticide)
The Theory of Evolution n In the 1960's after legislation to control the emissions of coal smoke, the level of pollution in English forests declined. The following graph represents the changes in smoke levels and the moth populations.
The Theory of Evolution THE FORMATION OF NEW SPECIES BEGINS WITH SMALL CHANGES n Divergence - accumulation of differences between groups; can lead to the formation of new species. n Speciation – process by which new species are formed.
The Theory of Evolution THE FORMATION OF NEW SPECIES BEGINS WITH SMALL CHANGES n Ecological Races – population of species that differs genetically because of adaptations to different living conditions. n Reproductive Isolation – prevention of mating between formerly interbreeding groups, or the inability of these groups to produce fertile offspring.
The Theory of Evolution Water Snakes of Lake Erie These three snakes show the full range of variation of the Northern Water Snake (Nerodia sipedon) across Lake Erie. The strongly banded morph is typical of N. sipedon throughout most of its range in North America. The slategrey morph is more typical of the populations found on the islands of the Lake Erie Archipelago, described as Nerodia sipedon insularum by Roger Conant and Richard Clay in 1937. The snakes show continuous variation among subpopulations, as illustrated by the intermediate morph. These snakes are unique to Lake Erie, and are not found on mainland Ohio, Michigan, or Ontario.
The Theory of Evolution On the mainland the snakes live in swampy marshy areas. Their skin is a combination of green and brown bands. These colors camouflage the snakes against predators. Off the coast are islands where the same species of snake have migrated. On the islands the color of the snakes are a bandless gray or an intermediate color between banded and unbanded colors. The shorelines of these islands are made up of mostly rocks like limestone. Once again being gray and unbanded on the island the snake is camouflaged and protected from predators. Birds such as herons and seagulls prey on the snakes. Snakes that have a phenotype (traits or adaptations) that give them an advantage will survive longer. This allows them to survive long enough to reproduce to pass their genes on to their offspring. It is possible that due to isolation that the snakes will evolve into different species. These snakes are endangered because of the human threat.